A method for dewatering sludges by use of an amine or mixture of amines having an inverse critical solution temperature with water is described and claimed in Emanuel, U.S. Pat. No. 3,899,419 issued Aug. 12, 1975 and assigned to the assignee hereof. Improvements in such method are disclosed in Ames, U.S. Pat. No. 3,925,201, and Peters, U.S. Pat. No. 4,056,466.
In addition, Ames et al., U.S. Pat. No. 4,002,562, named above teaches a method for breaking emulsions containing oil and water, and sludges containing solid matter, oil, and either bound water or unbound water. The method taught by Ames is applicable to a wide range of oil-water emulsions, including oil-in-water emulsions, and water-in-oil emulsions, and finds particular utility in the processing of waste emulsions, which have been difficult to process with known methods. According to the process taught in Ames '562, an amine, or mixture of amines, having an inverse critical solution temperature with water is added to an emulsion or sludge such that the temperature of the resulting mixture is at a temperature below the inverse critical solution temperature. If solid matter is present, it can be physically separated from the remainder of the mixture by a variety of known separation techniques, such as centrifugation or filtration. After separation of the solid matter, the remainder of the mixture is more or less a homogenous mixture of water, oil, and amine. When the temperature of the water-oil-amine mixture is raised above the inverse critical solution temperature of the amine, two components are produced: a water component containing small amounts of amine, and an oil-amine component containing small amounts of water.
Ames '562 provides for recycling of amine by removing the amine from the oil-amine mixture by known methods, for example, by distillation of the amine, leaving behind the oils. However, recovering the amine from the amine-oil mixture using known methods has proven to be very difficult and has resulted in unacceptable quantities of the amine remaining in the oil, particularly if the oil is to be recycled for further uses.
In practicing the process taught by Ames '562, the preferred amine, triethylamine, is removed from the oil-amine mixture by the low temperature distillation, leaving behind the non-volatile oil. Triethylamine has a normal boiling point of 89.8.degree. C. (vapor pressure equal to 760 mm#Hg), while an oil having a molecular weight of approximately 1,000 has a high boiling point with initial boiling starting typically at over 300.degree. C. and a smoke point in excess of 200.degree. C.
When the oil-amine mixture is heated moderately, for example by drying overnight at 105.degree. C., approximately 20 to 30%, by weight, of triethylamine remains in the oil. This result is accurately predicted by Raoult's Law. However, when the oil-amine mixture is heated to a temperature at which the mixture begins to smoke, for example 200.degree. C. or more, the triethylamine is not removed completely as expected. According to Raoult's Law, heating of the oil-amine mixture under such conditions would result in only approximately 0.8%, by weight, of amine remaining in the oil. In practice, however, approximately 8 to 15%, by weight, remains. Further heating does not remove the amine but instead leads to decomposition of the amine.
Thus, the methods known in the art for removing amine from an oil-amine mixture are unsatisfactory because they result in a loss of amine and contamination of the oil. There exists a need for a method of removing amine from an oil-amine mixture which does not result in a loss of amine and in which the resulting oil substantially amine-free.